Conventionally, pulse jet technology has been used for various print applications. Typically, pulse jet technology uses a plurality of piezo-electric crystals, where each piezoelectric crystal is connected to a corresponding element of a one- or two-dimensional array of nozzles. Upon electric excitation (or, equivalently fire pulse), each piezoelectric crystal forces viscous fluid through the corresponding nozzle to dispense a predetermined amount of the viscous fluid in a droplet.
Bubble jet technology is also widely used in existing printers. Typically, bubble jet technology uses a thermistor to heat a water-based ink very quickly to form a bubble that causes the ink to shoot from an element of a one- or two-dimensional array of nozzles. As the present invention can be applied to both pulse and bubble jet printers, the following discussion will be limited to only pulse jet printers. However, it should be apparent to one of ordinary skill in the art that the various embodiments of the present invention can be implemented in both pulse and bubble jet printers.
Due to operational uncertainty of conventional pulse jet printers, such as clogging of one or more nozzles, and due to the errors caused by the printhead driver electronics, the printed pattern may not be exactly the same as the intended pattern. In most of the printing applications, a level of such operational uncertainty may be permitted. However, for some applications, such as DNA microarray applications, even one missing spot (or, equivalently feature) may be critical to the quality of printing products. FIG. 1A is a perspective view of a typical substrate 100 bearing multiple microarrays 102, as produced by a conventional pulse jet printer.
FIG. 1B is an enlarged view of a portion of one microarray 102 of FIG. 1A, showing some of spots 104, where each microarray 102 can have more than one hundred thousand spots in an area of less than 20 cm2. Each spot 104 may carry a predetermined moiety or a predetermined mixture of moieties, such as a particular polynucleotide sequence or a predetermined mixture of polynucleotides. This is illustrated in FIG. 1C, where spots 104 are shown as carrying different polynucleotide sequences 106.
Polynucleotide sequences 106 may be formed using repeated steps of printing and chemical treatments. In each step, a nozzle may be fired on the corresponding spot 104 to mount a layer of one nucleotide during a sweep across the substrate. After chemical treatment of the mounted layer, the microarray is printed over again to mount the next layer of nucleotide during the next sweep, followed by another chemical treatment. The steps of printing and chemical treatments are repeated until the polynucleotide sequences 106 are obtained. Any missing layer of each polynucleotide sequence 106 may change the property thereof and, as such, the level of certainty about fluid placement from each nozzle is critical in the DNA microarray application. Existing microarray writers have additional optical systems to check if the spots 104 are properly generated. However, such optical systems cannot detect the missing layer(s) for each spot even though the spots can be detected.
Existing consumer printers are physically much smaller than a microarray writer and are not as susceptible to conditions that might cause a data transmission error. Thus, a current microarray writer checks the data from its printhead controller to printhead driver using a parity check, but does not check the data path from the printhead driver to the printhead. As a consequence, it cannot detect errors made on the printhead driver and/or in the communication to the printhead. Accordingly, there is a need for microarray writers with an ability to detect and/or prevent printing errors caused by the printhead driver electronics and/or communication to the printhead and provide assurance that the microarray writers are working correctly.